Properly Sizing a Datto Appliance



This article will help you determine the best-sized Datto business continuity device for your firm based on your data storage needs. We recommend that you review the information presented here before you upgrade or purchasing a Datto appliance.


  • Datto SIRIS
  • Datto ALTO
  • Datto NAS


Considerations for appliance sizing

When qualifying clients for a Datto appliance, it is important to consider both the current and future storage requirements.

For Datto NAS, calculate the average amount of storage space your production shares require, and use a 2x multiplier to determine your most optimal storage scenario.
  • How many machines will you need to protect?
  • Are these machines workstations or servers?
  • What is each machine's total protected size? To determine this amount, calculate the currently utilized space on the appliance, and then add a small cushion to account for future growth. You will need about 30% free space on the backed up hard drive to allow for optimal backups. The bare minimum is 20% (Though anything under 30% has the potential to throw errors during the backup process).
  • How much block level change will the system produce? Databases, separate database backups, log files, application, and files change on a daily basis.
  • Are you going to have encrypted agents? Encrypted agents should be treated as uncompressed and will take up more space.
We recommend that you underestimate this number, as block level changes take into account many more factors than just file changes: it also involves disk sector changes.
  • How often should you back up this system? Typically, Exchange needs an hourly backup, terminal servers require a daily backup, and backup domain controllers only require a few backups a week.
  • How far back would a client desire to go back for local, expedient restoration of files, folders, or entire operating systems?
  • If virtualized, how long would you need to run this machine off of the Datto device?
  • Does the client have expansion plans in place to possibly include additional servers or workstations?
  • What type of files are being backed up? Certain file types cause large changes when accessed for utilization or updating. Large databases, media files, or production workspaces can have large sizes and thus larger backup images.

Datto Best-Practices

The base recommendation for a Datto appliance is two times the total protected space of the agents that are to be protected, the "2-3x Multiplier Rule." The 2-3x multiplier ensures that the device will have the storage space needed to:

  • Store the first backup and then continuously roll this base image to the front of the chain with each backup.
Backups will start to fail as the appliance reaches near 100% full.
  • Provide storage space for backups to be stored according to Datto recommended retention policy:
    • One backup from each day for 7 days
    • One backup for each week for 60 days (~8 weeks). )
    • Delete local points after 60 days

Devices that fill up before the end of the retention policy for the device is reached result in failed backups.

  • Provides ample storage for local virtualization of agents.

When an agent is virtualized on a device, the ShadowShap agent continues to backup the virtualized system that is on the network. Since this is a technically a “new” device on the network, the next backup will be new base image. Depending on the size of the agent virtualized and the amount of local data change made during virtualization, your device could be filled very quickly if the 2-3x Multiplier rule is not being utilized correctly.

  • Ensure that space is available for the device's cloud synchronization.  

If there is not enough available space to create the offsite transfer file, the device could potentially have stalled cloud synchronization.

  • Provides a slight safety buffer for cases in which mild unexpected data growth could potentially occur over time.  

When a Datto device's Primary Storage Space reaches maximum capacity the optional resolution paths may be more difficult.

Encrypted Agents:

If you are planning to use encryption to protect your agents, please note that these backups are stored uncompressed. It may be advisable to look for a 3X multiplier when working with encrypted agents.

What happens if I don't have a large enough device?

The following problems result from not having enough space on your Datto appliance:

  • It fills quickly after deployment, blocking future backups.
  • Inability to maintain local and off-site backup chains.
While Datto Technical Support Engineers may be able to provide a temporary remedy, this situation will quickly come back until you upgrade the appliance or remove machines from its protection.

Figure 1: Device overview (click for larger image)

Assessing the Size of the Appliance

To check the size of the appliance, open its GUI. Access the Device Overview page.

Primary Storage represents the total used space. The used space is compared against the total available space for the calculated percentage.

  • Total Protected is the current size of all partitions that are currently selected for backup to the appliance.
  • Each protected system is further broken down to its space requirements. The number to the right of the agent name is the total space used per agent (Base plus recovery point snapshots)
  • The amount of space occupied by the associated recovery points is listed below the name of the protected system. 

When is it time to upgrade?

If you are experiencing failed local backups and are constantly sacrificing local backup retention in order to keep your system protected, it may be time to upgrade your device to the next size up.

As a rule of thumb, if your device is utilizing 85% of more of its local storage by backups, OR, if you do not have enough space to virtualize the volume of your largest agent of the remaining space, it may be time to discuss upgrading options.

Datto Hardware Resource Limitations

Devices don’t just need to be sized properly for storage. When choosing a proper device size, you need to make sure that the specifications of the device are in line with the machines that are to be backed up to it. Failure to do this can severely affect local virtualizations, as the virtualized machine will be seeking resources that are not physically available. This can lead to virtual machines running extremely slow and even high-resource programs crashing.

For example:

  • Client has a single server environment (Small Business Server) and the server runs the daily operations of the entire organization.
  • This server has 4 quad cores and 24 GB of RAM and the space that the server occupies is using an average of 225 GB.
  • If sizing the device on storage alone, the first reaction would be to purchase a S500 device to accommodate the space of the server. A S500 fits within the 2-3x multiplier perfectly, and even provides ample space for data growth.
  • However, should the server go down and clients need to run off of the server, the resources provided on the machine may not be able to power the machine in a sufficient state in order to allow for operations to continue.
  • A S500 has 16 GB of RAM and 4 CPUs total. The best possible scenario for the server to run would be 12 GB of RAM and taxing all 4 cores.
  • Since other device operations may need to continue (backups and other base device processes) there needs to be some resources still given to the device.

To ensure all of the device's features function properly, the client will want to consider a larger device that has more resources in order to allow for more resources to be considered for virtualization.

A "Real World" Sizing Scenario

A small client network has four machines that need to be protected:

  • Exchange Server: 250 GB
  • Application Server: 45 GB
  • Terminal Server: 60 GB
  • Workstation: 100 GB

The total protected space here comes out to 455 GB. This is on the border of an S1000 device with a terabyte of storage. For local backups, this should be a suitable purchase.  There are considerations to take into account:

How long do they want to maintain local data?

  • Do they have enough upstream bandwidth to get the images synced with the cloud on a consistent basis?
  • The recommendation is to have a MINIMUM of 100Kb/s upstream on a consistent, uninterrupted basis per terabyte of local storage. More is always advisable.

What happens if Exchange goes down?

  • If the Exchange server goes down and needs to be brought up locally on the Datto device via an instant virtualization, once that machine has been established on the network, the next backup will be a base image as the hardware platform has changed.
  • Factor in the next Exchange backup being 250 GB. That will cause your device to quickly fill up with an additional base image being present, not counting incremental changes subsequently
  • This may not be as pressing of a factor for smaller agents as there is less to backup should the machine need to be virtualized.

What kind of performance are they expecting to get out of these machines?

  • Considerations need to be made for the resources of the given machines
  • Depending on the resources of the protected machines, should they need to be virtualized, what kinds of processing power and RAM will be required for the machines to operate?
  • What is the daily activity level on each of the machines? How many people are accessing the machines on a regular basis?
  • Could the client survive with a virtual machine in an under-powered state that is being used in production?

If your specific sizing scenario is not covered here, contact your Datto Sales Executive for assistance.

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